Effect Of Oxygen Deficiency Research Articles

Evolution of Magnetocaloric Behavior in Oxygen Deficient La2/3Ba1/3MnO3−δ Manganites

Effects of oxygen deficiency on the thermomagnetic properties of La2/3Ba1/3MnO3−δ polycrystalline perovskites have been predicted. By the help of the phenomenological model, the temperature dependences of the magnetization for La2/3Ba1/3MnO3−δ with δ=0.0, 0.02, 0.05, 0.08, and 0.1 upon 1 T magnetic field were simulated. The behavior of the temperature dependent magnetocaloric effect, in the vicinity of magnetic phase transitions, was investigated. The magnetic entropy change, specific heat, and adiabatic temperature change for several δ were obtained. The values of maximum magnetic entropy change, full-width at half-maximum, and relative cooling power, in 1 T magnetic field variation, were calculated. As the oxygen content increases, the magnetocaloric effect of La2/3Ba1/3MnO3−δ , decreases and shifts to room temperature. The results obtained show a strong dependence on the oxygen deficiency of the materials. The magnetocaloric effect of these materials is large and tunable, suggesting a possible technical application of the materials at moderate magnetic fields near room temperature. It is shown that for La2/3Ba1/3MnO3−δ , the magnetic entropy change and adiabatic temperature change follows a master curve behavior.

Correlations between the oxygen deficiency and the laser damage resistance of different oxide films

Ta2O5, ZrO2 and HfO2 films are deposited on BK7 substrates by electron beam evaporation method. The effects of oxygen deficiency on the optical properties and laser-induced damage threshold (LIDT) are investigated by the combination of experimental methods and first principles calculations. The results show that the oxygen deficiency weakens the transmittance, whereas it enhances the absorption of all the films. Once the oxide vacancy appears, the band gaps decrease greatly, which seriously decrease the LIDT. The calculated negative vacancy energies indicate that, when the oxygen vacancy exists, Ta2O5 is most easily to be damaged, next is ZrO2 and the last is HfO2. It is consistent with the LIDT results that Ta2O5 increases 64.8%, ZrO2 increases 19.4% and HfO2 increases 12.9% when the oxygen vacancy is eliminated.

Bulk compound synthesis and oxygen deficiency effect on electronic and magnetic properties of the Zn-based oxyarsenide LaZnAsO1−δ

• Polycrystalline bulk compound LaZnAsO was synthesized for the first time. • Oxygen deficiency was introduced up to 35 at.% under a high pressure of 6 GPa. • The semiconductivity was highly robust against the oxygen deficiency up to 25 at.%. LaZnAsO has been studied mainly in the thin film form that was indicated as a wide-gap insulator with the gap size of ∼2.3 eV. We herein report the synthesis of polycrystalline bulk LaZnAsO compound for the first time under a high pressure of 6 GPa. Effect of oxygen deficiency on the electric and magnetic properties of the compound was also investigated by synchrotron X-ray diffraction and measurements of electrical resistivity, magnetic susceptibility, isothermal magnetization, and specific heat. The bulk LaZnAsO crystallized into the ZrCuSiAs-type structure with the space group P 4/ nmm , isostructural with the layered LaFeAsO . It is semiconducting with a thermal activation energy of ∼0.8 eV, and the semiconductivity was highly robust against oxygen deficiency up to 25 at.%. The virtue will benefit the development of a diluted magnetic semiconductor.

Metal–insulator transition in oxygen deficient Ti based oxide films

We have studied the effects of oxygen deficiency on the physical properties of Ti based oxide films (La2/3TiO3−δ, SrTiO3−δ, Ba0.2Sr0.8TiO3−δ). These films were obtained by pulsed-laser deposition and a noticeable oxygen deficiency, i.e. about 15% of oxygen missing, leads to very specific transport properties. Metallic or semiconductor behaviors are evidenced in the resistivity measurements as a function of temperature: a metal–insulator transition (MIT) is observed at low temperatures. Two different approaches have been used to interpret that MIT. For La2/3TiOx, the MIT can be described in the frame of the quantum corrections to conductivity (QCC) in disordered oxides. On the contrary, for Ba0.2Sr0.8TiOx or SrTiOx the MIT cannot be correctly fitted by the QCC model, and the resistivity curve with temperature is better described in the frame of the electron localization which can be classically modeled by the variable range hopping model.

Preparation and characterization of LiNi0.5Mn1.5O4−δ thin films taking advantage of correlations with powder samples behavior

The high voltage spinel LiNi0.5Mn1.5O4−δ films were obtained by pulsed laser deposition. The effects of oxygen deficiency, annealing treatment, and film thickness on microstructure, morphology and electrochemical properties were investigated. We showed that tuning the oxygen pressure and annealing treatment allows modifying the oxygen film stoichiometry. Trying to determine the oxygen stoichiometry in thin films, a series of oxygen-deficient spinel “LiNi0.5Mn1.5O4−δ” powder samples by quench steps from different temperatures were prepared. It is demonstrated that powders and thin films presenting similar cell parameters, namely related to the oxygen stoichiometry, show similar electrochemical profiles. Meanwhile, the compatibility of electrolyte with substrate and the stability of the target were also investigated.

Effect of oxygen deficiency on nitrogen assimilation and amino acid metabolism of soybean root segments

Plants submitted to O(2) deficiency present a series of biochemical modifications, affecting overall root metabolism. Here, the effect of hypoxia on the metabolic fate of (15)N derived from (15)NO(3)(-), (15)NO(2)(-) and (15)NH(4)(+) in isolated soybean root segments was followed by gas chromatography-mass spectrometry, to provide a detailed analysis of nitrogen assimilation and amino acid biosynthesis under hypoxia. O(2) deficiency decreased the uptake of the nitrogen sources from the solution, as ratified by the lower (15)NO(3)(-) and (15)NH(4)(+) enrichment in the root segments. Moreover, analysis of endogenous NO(2)(-) and (15)NH(4)(+) levels suggested a slower metabolism of these ions under hypoxia. Accordingly, regardless of the nitrogen source, hypoxia reduced total (15)N incorporation into amino acids. Analysis of (15)N enrichment patterns and amino acid levels suggest a redirecting of amino acid metabolism to alanine and γ-aminobutyric acid synthesis under hypoxia and a differential sensitivity of individual amino acid pathways to this stress. Moreover, the role of glutamine synthetase in nitrogen assimilation both under normoxia and hypoxia was ratified. In comparison with (15)NH(4)(+), (15)NO(2)(-) assimilation into amino acids was more strongly affected by hypoxia and NO(2)(-) accumulated in root segments during this stress, indicating that nitrite reductase may be an additional limiting step. NO(2)(-) accumulation was associated with a higher nitric oxide emission. (15)NO(3)(-) led to much lower (15)N incorporation in both O(2) conditions, probably due to the limited nitrate reductase activity of the root segments. Overall, the present work shows that profound alterations of root nitrogen metabolism occur during hypoxic stress.

Effect of oxygen deficiency on the magnetic field-dependent entropy in YBa2Cu3O7−δ

Roulin et al (1988), in one of their experimental papers, have presented a study of field-dependent entropy of high-purity YBa2Cu3O7 − δ (YBCO) as a function of oxygen deficiency. In order to explain their experimental results, we have used phenomenological GL-theory of anisotropic HTSCs in the London limit in line with of our earlier paper (Pattanaik et al, Physica B405, 3234 (2010)). Moreover, to account for the applicability of the theory at high field, we have incorporated the effect of vortex overlapping in the London theory done by Nanda (1995). Here, we have presented the variation of change in entropy (ΔS) with magnetic field for different oxygen deficiencies δ = 0, 0.04, and 0.06. On comparison, we found that our results are in good agreement with the experimental data of Roulin et al (1988). The variation of penetration depth (λ) and anisotropic ratio of effective masses (γ) with concentration is also presented.

Effect of oxygen deficiency on room temperature ferromagnetism in Co doped ZnO

We investigated the correlation between magnetization and oxygen vacancies in Zn0.95Co0.05O nanoparticles. Enhanced magnetizations were found in SiO2 nanopowders and carbon nanotubes (CNTS) treated Zn0.95Co0.05O, which are attributed to minimizing nanoparticle size and increasing oxygen vacancy concentration. After oxygen annealing, the magnetization of both non-treated Zn0.95Co0.05O and CNTS treated Zn0.95Co0.05O decreased sharply with the filling of the oxygen vacancies, while the SiO2 treated Zn0.95Co0.05O was influenced little as the amorphous SiO2 shell prevents the diffusion of oxygen into magnetic particles. It demonstrated that the ferromagnetism comes from the interfacial oxygen deficiency and is tunable by changing the oxygen vacancies.

The Influence of Defects on Mo‐Doped TiO2 by First‐Principles Studies

TiO(2) doped with transition metals shows improved photocatalytic efficiency. Herein the electronic and optical properties of Mo-doped TiO(2) with defects are investigated by DFT calculations. For both rutile and anatase phases of TiO(2), the bandgap decreases continuously with increasing Mo doping level. The 4d electrons of Mo introduce localized states into the forbidden band of TiO(2), and this shifts the absorption edge into the visible-light region and enhances the photocatalytic activity. Since defects are universally distributed in TiO(2) or doped TiO(2), the effect of oxygen deficiency due to oxygen vacancies or interstitial Mo atoms is systemically studied. Oxygen vacancies associated with the Mo dopant atoms or interstitial Mo will reduce the spin polarization and magnetic moment of Mo-doped TiO(2). Moreover, oxygen deficiency has a negative impact on the improved photocatalytic activity of Mo-doped TiO(2). The current results indicate that substitutional Mo, interstitial Mo, and oxygen vacancy have different impacts on the electronic/optical properties of TiO(2) and are suited to different applications.

Effects of seedbed properties on crop emergence. 4. Inhibitory effects of oxygen deficiency

For studies of the effects of seedbed properties on crop emergence, experiments were carried out in shallow plastic boxes. In some experiments, it was examined whether rainfall after sowing could cause oxygen deficiency in the seedbed sufficiently severe to hamper emergence. Crops studied were barley (Hordeum vulgare L.), wheat (Triticum aestivum L.), oilseed rape (Brassica napus var. oleifera, L., Metzg.) and pea (Pisum sativum L.). For harmful oxygen deficiency to develop it appeared that rainfall would need to cause structural collapse of the surface layer followed by continuously wet weather accompanied by slow drainage and high oxygen consumption in the soil; in the experiments the latter was achieved by large amounts of easily decomposable organic matter. It was concluded that such conditions are rare in the field. Therefore, unless rainfall after sowing generates surface water for an extended period, the poor crop emergence often observed after such rainfall is nearly always caused not by oxygen deficiency, but by surface layer hardening when this layer dries.

自己熱制御材料用La1-xSrxMnO3-δ薄膜の金属-絶縁体相転移に及ぼす残留応力と酸素欠損の影響

自己熱制御材料用La1-xSrxMnO3-δ薄膜の金属-絶縁体相転移に及ぼす残留応力と酸素欠損の影響

Effect of oxygen deficiency on the photoresponse and reactivity of mixed phase titania thin films

Nonstoichiometric mixed phased titania nanocomposites (TiO2−x) were deposited by reactive direct current magnetron sputtering. The authors explored the role of nonstoichiometry (as defined by oxygen deficiency in synthesis) in mixed phase titania thin films and its effects on the photoresponse and photocatalytic performance for CO2 reduction to methane under UV and visible light. Oxygen partial pressure was varied during film deposition, yielding different levels of oxygen deficiency in the films. Optimized nonstoichiometric films showed a strong redshift. The authors have identified an optimum set of synthesis conditions for TiO2−x films that produce a relative maximum in photocatalytically produced methane under both UV and visible light.

Effect of oxygen deficiency on optical band gap shift in Er-doped ZnO thin films

Er-doped ZnO films were deposited by reactive magnetron sputtering technique at different oxygen flow rate. The microstructures, the chemical state of the oxygen and the optical absorption properties of ZnO:Er films were investigated. The X-ray diffraction spectroscopy (XRD) results and the X-ray photoelectron spectroscopy (XPS) analyses about the oxygen in the doped samples indicated that oxygen flow rate has great effect on the crystalline quality of ZnO:Er films. It was concluded that the decrease of the crystalline quality of the samples was caused by the oxygen deficiency. The optical absorption properties and the shift of the optical band gaps were investigated. The analysis reveals that the blue shift of the band gaps was caused due to the decreasing of O 2−ions at the intrinsic sites and the increasing of O 2-ions at the oxygen deficient regions.

Oxygen deficiency effect on resistive switching characteristics of copper oxide thin films

In this Letter, bilayered Cu 2O/CuO thin films were grown on Nb doped SrTiO 3 (Nb:STO) substrates by plasma assisted molecular beam epitaxy. The current–voltage characteristics of Pt/Cu 2O/CuO/Nb:STO devices show reproducible and pronounced current–voltage hysteresis which was induced by the CuO/Nb:STO junctions. By comparing the current–voltage curves of the bilayered and single-layered CuO thin films, we attribute the prominent switching behavior to the oxygen-vacancies-mediated-carriers-trapped-detrapped process with the aid of the applied forward (reversed) bias voltage.

Effect of vacancy-type oxygen deficiency on electronic structure in amorphous alumina

Electronic and atomic structures associated with a vacancy-type oxygen deficiency in an amorphous alumina model are studied by first-principles calculations. The energy levels of the oxygen defects significantly shift depending on their charge states because of remarkable changes of local atomic structures. That is different in character from the α crystal case. We discuss a possibility of the oxygen defects as a conductive path and present an atomistic mechanism of the resistive switching effects in the memory devices.

Effect of small oxygen deficiency on the para-coherent transition and 2D–3D crossover in untwinned YBa 2Сu зО 7− δ single crystals

We investigate the influence of the disorientation angle between the direction of a constant magnetic field (up to 15 kOe) and the ab-plane α ≡ ∠( H,ab) to the temperature dependence of the excess conductivity in the temperature interval of the transition to the superconducting state in untwinned YBa 2Cu 3O 7− δ single crystals. We discuss the appearance of low temperature “tails” (para-coherent transitions) on the resistive transitions, corresponding to different phase regimes of the vortex-matter state. At temperatures above the critical temperature, the temperature dependence of the excess para-conductivity is interpreted within the Hikami–Larkin theoretical model of the fluctuation conductivity for layered superconductors.

Structural parameters and X-ray Debye temperature determination study on copper-ferrite-aluminates

The compositional dependence of structural parameters and X-ray Debye temperature for CuAl x Fe 2− x O 4 ( x = 0.0, 0.2, 0.4 and 0.6) spinel ferrite system has been studied by means of X-ray powder diffraction (XRD) patterns analysis at 300 K. The XRD data have been used to determine the lattice constant, X-ray density, distribution of cations among the tetrahedral and octahedral sites of spinel lattice, oxygen positional parameter, site radii, bond angle, bond length and interionic distances. The X-ray Debye temperatures have been determined from integrated intensities of selected Bragg reflections. It is found that Al 3+-substitution has marked influence on various parameters. A deficit of Cu 2+-cations at the octahedral sites of the spinel lattice leads to the absence of co-operative active Jahn–Teller distortion and the crystal structure retains into cubic. The increasing disagreement between observed and calculated intensities and reduction in intensity of diffracted beam with increasing Al-concentration have been explained based on preferred orientation and extinction effects. The effect of oxygen deficiency on intensity ratios of planes has been discussed in brief.

Impact of hypoxia on consumption of Baltic cod in a multispecies stock assessment context

Summary The Baltic Sea is characterised by a heterogeneous oceanographic environment. The deep water layers forming the habitat of Baltic cod (Gadus morhua callarias L.) are subjected to frequently occurring pronounced anoxic conditions. Adverse oxygen conditions result in physiological stress for organisms living under these conditions. For cod e.g. a direct relationship between oxygen availability and food intake with a decreasing ingestion rate at hypoxia could be revealed. In the present study, the effects of oxygen deficiency on consumption rates were investigated and how these translate to stock size estimates in multi-species models. Based on results from laboratory experiments, a model was fitted to evacuation rates at different oxygen levels and integrated into the existing consumption model for Baltic cod. Individual mean oxygen corrected consumption rates were 0.1–10.9% lower than the uncorrected ones. At the currently low predator stock size, however, the effect of oxygen-reduced consumption on the total amount of eaten prey biomass and thus predation mortalities was only marginal. But should successful management lead to higher cod stock sizes in the future, then total predation mortalities will greatly increase and thus improved precision of these estimates would be valuable for the assessment of prey stocks.

Effects of oxygen deficiency in the sol–gel ZrOx film on the electrical properties of Au/ZrOx/n-type Si/In devices

The ZrOx permittivity and leakage currents through Au/ZrOx/n-type Si/In structures are studied. The electrical conduction investigations suggest that the leakage behaviour is governed by the Schottky emission. The leakage current strongly depends on the O/Zr atomic concentration ratio of ZrOx films and an increase in the number of oxygen-vacancy-related defects may result in a decrease in the ZrOx permittivity, enhancing the leakage conduction of the Au/ZrOx/n-type Si/In devices. In addition, the discrepancy in the ZrOx permittivity determined in the current density-electric field and capacitance–voltage characteristics is attributed to the formation of the intermediate ZrSixOy layer.

Oxygen-deficient effect on charge ordering in spin- and charge-frustrated ferriteYFe2O4−δ

The effects of oxygen deficiency on charge ordering were investigated by transmission electron microscopy at various deficiencies and temperatures of ${\text{YFe}}_{2}{\text{O}}_{4\ensuremath{-}\ensuremath{\delta}}$. We found that the detailed nature of the charge ordering structures is associated with changes in the superlattice reflections and diffuse scattering. They go from (1/3 1/3 1/2)-type superlattice reflection to $(1/3\phantom{\rule{0.3em}{0ex}}1/3\phantom{\rule{0.3em}{0ex}}l)$-type straight-type diffuse scattering, then to zigzag-type diffuse scattering. With the oxygen deficiencies increased, the interchange correlation of Fe-O bilayers obviously decreases, yet the triple superperiodicity along ${[110]}^{\ensuremath{\ast}}$ remains unchanged. These findings on frustrated ferrites indicate the stability of in-plane threefold charge ordering and the importance of the interchange interaction between bilayers in the structural phase transitions.